How is Stack implemented in STL?

Question

I came across this:

Standard C++ Containers

It triggered me the question, how are stacks implemented in STL?

I am looking for a description similar to:

How is C++ std::vector implemented?

What really is a deque in STL?

Answer 1

stack is an adapter which uses another container for the underlying storage, and links the functions push , pop , emplace etc. to the relevant functions in the underlying container.

By default, std::stack uses std::deque as underlying container. But you can specify your own, eg std::stack<T, std::vector<T>> s; .

For more details about this, see cppreference .

Answer 2

std::stack has a template parameter Container , which is required to be a container that can store elements of type T (that is to say, the type of the elements of the stack). This container is required to have back() , push_back() and pop_back() functions, and the standard containers vector , deque and list all satisfy the requirements.

So, whichever container type the user specifies, the resulting instantiation of std::stack is a class which:

• has a data member of type Container<T> (or something very similar if not literally a data member. I suppose it could probably be a private base class).
• calls push_back() on the container whenever you call push() on the stack.
• calls pop_back() on the container whenever you call pop() on the stack.
• and so on.

Loosely speaking, std::stack<T> is an object that wraps up an instance of std::deque<T> , and hides most of deque 's functionality in order to present a simpler interface solely for use as a last-in-first-out (LIFO) queue. Similarly std::queue presents a FIFO queue.